1. Field of the Invention
The invention relates to a clamping head for winding tubes. More particularly, this invention relates to a clamping head which utilizes both an axially movable slide block and a pivotally movable thrust member to provide uniform expansion and contraction action relative to the inner surface of a tube or core, such as is used in the papermaking industry to begin formation of wound rolls of paper or board.
2. Description of the Prior Art
Such a clamping head, which is sometimes called a core chuck in the papermaking industry, is known from German patent publication DE 1 574 438 B. It is used for winding material in web form, such as paper webs and the like, onto winding tubes, and also for winding off from such winding tubes. A clamping head is selectively engageable with each tube end, in a central, essentially circular recess, in order to transmit the torque necessary for winding-on or controlled winding-off to or from the winding tube. In the papermaking industry, such tubes are sometimes called cores or reel spools.
In the case of the above-referenced known clamping head, a hexagonal clamping head shank is provided that is encompassed by clamping pieces in the form of segments. The radial inner surfaces (contact surfaces) of the clamping pieces abut, in planar fashion, the six outer surfaces of the clamping head shank while in their non-expanded, resting position where they do not engage the tube. The radial outer surfaces of the clamping pieces, which are subsequently made to fit in the recess of the winding tubes, form, in the resting position, a periphery that is normally less than the overall circumferential length of the recess at the end of the winding tube. The clamping pieces and the clamping head shank can be rotated relative to one another. In this way, the clamping pieces can be pressed in a radially outward direction along their overall length looking to the axial direction of the clamping head, so that their outer surfaces spread non-positively in the recess of the winding tube. As the web is wound-on progressively, the roll diameter, and thus the torque to be transmitted, increases. This automatically leads to an increased expansion of the clamping pieces. However, it is not necessarily possible, upon completion of the winding-on or winding-off process, to muster the same maximum torque between the tube, or the roll, and the clamping head in the opposite direction as had occurred during the winding process in the original direction. It is not possible, therefore, to loosen or to readjust the expander. The clamping heads must therefore be withdrawn axially from the winding tube in their expanded operating position using great force.
Drawing the winding tubes off the clamping head using a different clamping head design, as described inter alia in German patent publication DE 28 15 310 C, is easier than utilizing the clamping heads of the type previously mentioned because with this other known clamping head design, instead of torsion, there is an axial movement between the clamping head shank and the clamping pieces in order to achieve expansion or contraction of the clamping pieces. For this purpose, the sliding surfaces between the clamping head shank and the clamping head pieces are wedge-shaped. An axial stop connected to the clamping pieces, which axial stop abuts the tube face when the clamping pieces are not yet expanded, enables a force in the axial direction to be transmitted through which the clamping pieces slide along the clamping head shank and so expand in the recess at the winding tube end. In doing so, the expansion distance that is constant along the whole of the clamping length depends on the magnitude of the sliding-in force applied in the axial direction. When the clamping head is axially withdrawn from the winding tube, the clamping head shank initially retracts relative to the clamping pieces, and the clamping pieces move in a radially inward direction. As a result, the radial force of pressure abates. With this clamping head design, it is easier, therefore, to withdraw the clamping head from the winding tube than it is with the prior-art type clamping heads previously mentioned. However, along with this advantage goes, inter alia, the disadvantage that the clamping force depends exclusively on the axial force exerted on the clamping heads. If this is excessive, the winding tubes become distorted; if it is not sufficient, then as the torque increases, there is the danger of slippage between winding tube and clamping head. Neither is desirable.
The relative position between the clamping pieces, and therefore the winding tube as well, and the clamping head shank is necessarily variable and undefined in the case of clamping heads of this second prior-art design. Generally speaking, however, this is not desirable.